Chapter Seven

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Chapter Seven

• Heredity and Breeding

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Breeding and Husbandry

• Genetics deals with heredity.
• why offspring resemble or differ from their
  parents
• Similarities and differences
• due to heredity
• caused by environmental factors or mutations
• Successful breeding of animals depends on
• an understanding of basic genetics
• breeding system that suits the needs of a
  particular protocol.

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Genes Chromosomes

• Physical characteristics of organisms are passed
  from one generation to next by genes.
• an inherited characteristic such as fur or eye
  color, number of toes or the length of the
  intestine
• Genes are on chromosomes made of DNA.
• Chromosomes paired structures in cell nuclei.
• Number of pairs differs for various species.
• Normal members of a species have number of
  pairs.
• Only ova sperm chromosomes are not paired.
• When the ovum is fertilized by the sperm, the
  zygote forms paired chromosomes from the unpaired
  sets.
• Half of each parents genes passed to next
  generation.

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Expression Mutation

• Expression is result of
• interaction of paired genes.
• Genes can be either dominant or recessive.
• Recessive brown fur gene dominant black fur
  expression of dominant black gene (black fur).
• Gene may mutate when passed parent to offspring.
• Mutations may occur spontaneously or by chemical
  physical environmental factors.
• Can be either harmful or beneficial.
• Such animals have potential use as a model to
  help understand diseases or phenomena.

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Reproduction

• 1st step in sexual reproduction is production of
  sperm eggs.
• Fertilization location/manner depend on species.
• In most mammals fertilization occurs within s
  reproductive tract.
• In other types of animals, it occurs outside the
  body.
• Development site also depends on species.
• In most mammals, zygote becomes implanted grows
  in the uterus.
• In birds and reptiles, embryonic development
  usually occurs outside body, inside an egg.

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(Image) Female Internal Reproductive Organs
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Gestation Estrus

• Time required for a zygote to develop into a
  fetus be born gestation period.
• Natural end of gestation period called
  parturition.
• Males produce sperm continually are ready to
  mate almost any time after reaching maturity.
• Females mate only during specific times.
• During estrous cycles, females eggs undergo
  changes which prepare them for fertilization.
• During estrus the female allows mating.
• Ovulation usually occurs at or near this time.
• Cells in vaginal wall change in phases of cycle.
• In some species samples can be collected from the
  vagina examined to determine phase of estrous
  cycle.

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(Image) Embryonic Growth Phases
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Breeding Schemes

• Breeding schemes determine how similar or
  different parents are from offspring.
• Scheme depends on animal requirements.
• Inbreeding is used to produce animals with
  minimal genetic variation.
• share characteristics are identified as
  specific strain
• Strains are inbred after gt20 generations.
• Rodents are the most frequently inbred animals.
• C57BL, DBA/2, C3H, and BALB/c
• A mating to an unrelated animal or a different
  strain contaminates the inbred line.
• Escaped animal should not be returned to a cage.

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Breeding Schemes II

• Outbreeding is a scheme of breeding in which only
  unrelated animals of the same stock are mated.
• Frequently used in rodent colony management.
• Results in maximum genetic difference among
  animals.
• Usually more vigorous animals larger litter
  size.
• CF1, ICR, and Swiss
• Other breeding schemes
• usually involve mating for
• desirable characteristics.
• Animals share a common ancestor line breeding.
• Cross breeding mating animals of different
  breeds.

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Mating Systems

• After determining genetic type required for a
  project selecting mating system appropriate to
  species being used, more than one mating system
  may be appropriate.
• depends on management considerations
• Monogamous mating 1 1 paired together
  for the duration of their breeding life.
• Simplifies record keeping lends itself well to
  maintaining inbred or outbred colonies.
• Gerbil is bred most successfully with monogamous
  pairs.

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Harem Mating

• Polygamous mating system 1 with gt 2 s
• results in large of young from least of
  breeders
• economical method of production
• difficult to keep accurate records
• s often share nursing responsibilities, causes
  uncertainty of which female gave birth to
  offspring.
• for colonies when not critical to know which is
  the mother
• Cage must be large enough for adults and young
  until offspring are weaned.
• Separate housed are together for
  breeding.
• Reduces of animals needed, permits accurate
  record keeping, but labor costs are high.
• Used when s kill the young or are
  aggressive.

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Other Breeding Concerns

• Consideration should be given to selection of
  good breeding stock.
• Animals should be healthy, young nonaggressive.
• Females should exhibit good mothering
  characteristics adequate milk production.
• The health of breeding animals must
• be monitored and sign of illness or
• disease should be reported immediately.

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Maintenance of Breeding Animals

• Rodents rabbits may desert, kill or cannibalize
  their young if disturbed.
• Delay cage changes for a few days following
  birth.
• Minimal handling of newborn animals is a general
  rule.
• Wean 21 days of age in rats and mice.
• Rodents build nests if provided soft paper,
  shredded wood fiber or cotton.
• Rabbits require a nest box pull hair to line
  nest.
• 1214 hours of light is best for
• rodent breeding colonies.
• The longer light period helps
• establish consistent estrous cycles.

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Record Keeping

• The following are examples of information that
  could be kept for a breeding colony
• Breed, strain and type of animal
• Parentage or ancestry
• Animal identification number
• Sex
• Date mated
• Date of birth and number of offspring
• Date weaned and number of offspring
• Sex of young
• Veterinary information

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Animal Identification

• Identify individual animals.
• critical for determining parentage and lineage
• Mixing animals in a cage or placing an animal in
  a different cage without proper identification
  can be devastating to a research project.
• Cage cards are used to
• identify each animal or
• group of animals.
• Card contains information about
• history, genetic background,
• IACUC , type of experiment contact.

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Short-Term ID

• Clipping or shaving various
• locations or patterns
• Nontoxic, waterproof dyes or markers
• Markings, colors, sex, hair or breed
• Collars for cats, dogs and nonhuman primates
• Must be routinely checked as animal grows.
• Loose-fitting collar could get snagged on cage.
• Dogs and cats purchased from commercial suppliers
  have a USDA number on record.
• USDA tag may be left on collared animals.
• Collars may cause skin irritation strangulation
  interfere with neck bandages other apparatus.

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Permanent Identification Methods

• Implantable microchip transponders transmit ID.
• Subcutaneous chip implanted
• Recording device scans chip and reads
• Ear notching holes at various positions
• Notches holes a numbering code.
• Easy to read and produces little trauma to
  animal.
• Used in pigs rodents, not hamsters guinea
  pigs.
• Holes or notches close over a period of time.
• Sanitize punch tool between animals.
• Toe clipping must have strong justification.
• removal of 1st bone of certain toes a code
• gttime, gtdifficult, gtstress than ear marking
• Anesthesia is recommended.

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Ear Wing Tags

• Small metal clips are stamped with individual
  s.
• Using special pliers, they are applied near the
  base of the ear or to the wing.
• Procedure is quick and causes minimal pain.
• Used on rodents, rabbits, sheep birds.
• As with ear notching, the ID can be lost.
• In birds a numbered leg band is an alternative to
  a wing tag.

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Tattooing

• 2 types of tattooing devices
• Hand-operated instrument clamps onto ear so
  pointed tips pierce skin and ink dyes the
  underlying tissue.
• Electrical pen-like tool has a reciprocating
  multi-point needle which marks the skin.
• Ink is massaged into skin perforations.
• Clean disinfect instruments between animals.
• Ear tattoo ID in rabbits
• Avoid damage to medial artery or marginal ear
  vein.
• Use black ink on lighter colored breeds.
• Green ink on dark-colored breeds
• Tattoo may spread as animal grows, making the
  tattoo unreadable and tattoo may have to be
  redone.

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Tattooing Continued

• Ears - g. pigs, cats, dogs, monkeys ungulates
• Dogs - ears, skin of flanks or oral cavity
• Dogs anesthetized and tattoo area is clipped,
  washed dried.
• Nonhuman primates - chest or inner thigh
• Even individually housed animals should be
  tattooed a cage card posted w/ all other info.
• Neonatal rats mice may be permanently IDd
• by injecting tattoo ink subcutaneously
• into ears, tail, hocks or toes, using
• a series or pattern of dots.

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Additional Reading

• Nicholas, F.W. Veterinary Genetics. Iowa State
  University Press, Ames, IA. 1987.